HOLOBIONTnoun ho·lo·bi·ont (ˈhō-lə-bī-ŏnt) (Greek, from holos (όλος), whole; bios (βίος), life; -ont, to be; whole unit of life): The basic and strict definition of holobiont is that it is a host organism (plant or animal) in interaction with all associated microorganisms as an entity for selection in evolution.. ﻿﻿Holobiont describes a long-term physical association between different living organisms encompassing all symbiotic associations, including parasites, mutualists, synergists, and amensalists.